The human olfactory epithelium normally retains the life-long capacity to make new olfactory sensory neurons to maintain sensory function or restore it after injury. In some aged individuals, that capacity is lost, because the normal stem cells responsible for neurogenesis become exhausted. There is also a population of reserve stem cells, called horizontal basal cells (HBCs), which are activated by injury to restore neurogenic capacity, but do not activate with mere stem cell exhaustion. A method to induce these reserve stem cells to replenish olfactory neuroepithelium under different circumstances would be useful in the treatment of various olfactory disorders.